working in Istanbul as foreigner

I need an advice from the guys who are working here in Istanbul as a foreigner.

A friend of mine (American who has PhD and has pharmaceutical company experience) is considering coming Istanbul and finding a job in a pharmaceutical company. Do you think turkish knowledge is a kind of obligation to find a job here or what is the possibility to get a job here as foreigner, what are the challenges or advantages?

Well, as Turkish I have never thought in this way and actually have no idea. I really appreciate if you could share your similar experiences or opinions, since I am expected to provide a feedback soon.